Down syndrome occurs when abnormal cell division results in an extra copy of the 21st chromosome. Most people have 46 chromosomes, while people with Down syndrome have 47. This extra genetic material is what causes the developmental delays and characteristics associated with the condition.

There are three types of Down syndrome: Trisomy 21 (nondisjunction), translocation and Mosaicism. Trisomy 21 occurs when there are 3 copies of the 21st chromosome (instead of the normal 2) in all cells. It is the most common (this is what Noah has) and occurs in 95% of instances. Translocation occurs when a piece of the 21st chromosome attaches to another chromosome. Translocation makes up between 3-5% of Down syndrome cases and is the only form that can be inherited. Mosaicism is where not all of the cells in the body carry the extra chromosome. It occurs in 2-5% of Down syndrome cases. A person with Mosaic Down syndrome may exhibit all, some or none of the characteristics of Down syndrome depending what percentage of cells carry the extra chromosome and where the cells are located.

Down syndrome is named after John Langdon Down, an English physician, who was the first to fully describe the syndrome in 1866. The National Down Syndrome Society (NDSS) has a great page that highlights some of the myths commonly associated with Down syndrome: http://www.ndss.org/Down-Syndrome/Myths-Truths/

What causes Down syndrome?

Down syndrome is caused by an error in cell division called nondisjunction. This abnormal cell division occurs at conception and it is not known why this happens. Down syndrome is not related to race, nationality, religion or socioeconomic status. The incidence of Down syndrome increases with advancing maternal age, but researchers don’t understand exactly why this is the case.

What are some characteristics typical of people with Down syndrome?

One of the most important facts to know about individuals with Down syndrome is that they are more like others than they are different. However, there are several characteristics typical of people with Down syndrome.

Physical characteristics can include a small chin, slanted eyes, hypotonia (low muscle tone), epicanthal folds (extra crease in the inner corner of the eye), flat nasal bridge, single crease of the palm, low-set ears, Brushfield spots in the eye, short limbs, excessive joint flexibility, Clinodactyly (inward curve of the pinky finger) and extra space between the big toe and second toe. However, not all individuals with Down syndrome have all of these characteristics and they don't all look the same. Kids with Down syndrome often look more like their siblings than they look like other kids with Down syndrome.

Cognitive delays are pretty much universal for individuals with Down syndrome. Intellectual disability generally varies from mild to moderate, but there is a wide variety of abilities within the population that are impossible to predict ahead of time. People with Down syndrome often have a high social and emotional intelligence. We already see this with Noah, as he is a very social baby and is extremely engaged when you talk to or smile at him.

There are also health problems that often go along with Down syndrome, including congenital heart defects, hypothyroidism, gastrointestinal issues, hearing loss, vision problems, sleep apnea, Alzheimer’s disease, celiac disease, autism, childhood leukemia and seizures. As you can imagine, we were quite overwhelmed when we first read this list after receiving Noah’s diagnosis. We are blessed that so far Noah only has hypothyroidism (easily treatable) and moderate hearing loss, which will hopefully be resolved when he is old enough to get tubes in his ears.

How common is Down syndrome?

I was surprised to find that one in approximately every 700 babies in the US is born with Down syndrome. It the most frequently occurring chromosomal disorder. According to the NDSS, approximately 400,000 Americans have Down syndrome and about 6,000 babies with Down syndrome are born in the US each year. Sadly, over 90% of pregnancies with a Down syndrome diagnosis are terminated.

Is it Down, Downs or Down's?

The correct term is Down syndrome, not “Downs” and the “S” in syndrome is not capitalized. On my site I will sometimes abbreviate it to DS because it’s easier than writing it out each time. Some people prefer the abbreviation Ds or T21 (Trisomy 21) instead.

We like to use what is called “People-First Language” when we talk about Down syndrome or any other disability. Noah is a baby with Down syndrome, not a “Downs baby”. He is a child first. We also prefer the word “typical” to “normal” when referring to typically developing children. Words are powerful and the meanings we attach to them can drive social perception, attitudes and feelings. Often unintentionally, we devalue a person by labeling them with their disability first. But don’t worry, we understand that not everyone is aware of the correct terminology so we won’t be upset if you refer to Noah as a Downs baby!

There is a lot we are learning about Down syndrome each day. We will continue to update this page as we find out more!